1. Field of the Invention
The present invention relates to optical data busses. More specifically the present invention relates to a novel and improved optical data bus utilizing a plurality of small, lightweight optical RF bandpass filters each for extracting a particular input signal from a composite signal comprised of all input signals.
2. Background Art
Future tactical data links, including data busses, electronic intelligence collection systems and high resolution radar receivers demand high performance, large time-bandwidth product devices for signal processing. Fiber and integrated optics technologies promise to provide versatile and effective signal processing techniques with bandwidths and time-bandwidth products exceeding those of any other technology currently envisioned. Other potential benefits include low power requirements, reduced size, weight, cost, complexity and reduced sensitivity to electromagnetic interference, electromagnetic pulse and nuclear radiation. Another potential benefit especially with respect to an optical data bus is the virtually unlimited expansion capability, limited only by the number of input RF carrier frequencies and the assigned bandwidths associated with each carrier frequency.
Previous attempts at constructing fiber optic RF frequency multiplexed data buses have attempted to use different optical carrier frequencies for the multiplexing. In implementing such a system, multiple optical carrier frequencies must be generated in which a series of complex filters, polarization discriminators, and modulators are used to generate the combined multiplexed signal for transmission over a single optical fiber. The demodulating scheme includes polarization discriminators, filters, and detectors for isolating the different modulated carrier signals and detecting the modulation on each carrier signal. These systems have the inherent disadvantage that a plurality of different optical carriers must be generated. Another disadvantage of these systems is that a great number of components must be utilized to achieve a working system thereby resulting in significant increases in cost, size, and weight.
With respect to optical filters used in optical systems, it is known to construct a segment of optical fiber which is resonant to the optical or carrier frequency by placing highly reflecting mirrors on both ends of the fiber and injecting light of appropriate characteristics into the fiber. A fiber segment so configured may be referred to as a resonant cavity with respect to the carrier frequency. This resonant cavity has been described as being useful for the determination of coupling coefficients so as to enable one to specify and predict the light transmission characteristics of a particular fiber. This test assumes the use of a multimode fiber segment where the coupling coefficients between at least two light propagating modes are simultaneously at resonance within the fiber segment when measured. However, it has not been suggested prior to applicant's above-referenced co-pending application entitled "Optical Recursive Filter" that a multimode optical fiber functioning as a resonant cavity may be employed, with its attendant advantages relating to cost, size, weight and reduced susceptibility to external interference, as an RF bandpass filter, especially with respect to an RF frequency multiplexed optical data bus.